The full-load testing of internal combustion engines at maximum safe speed can be accomplished by connecting the engine to a dynamometer capable of absorbing the full-load output of the engine and capable of measuring the speed, torque and horsepower of the engine. Dynamometers are very large, very expensive, and very inconvenient to use.
A much more economical and convenient apparatus for testing internal combustion engines under simulated full-load conditions is apparatus for operating the engine with all but one of n ignitions interrupted, where n may be greater than the number of cylinders, so that all cylinders are operated in sequence under full power conditions. The engine operates at full speed driving frictional and pumping loads, without danger of overspeeding and damaging the engine. Such apparatus is described in Pat. No. 3,757,570, issued on Sept. 11, 1973, to Cowley and Hulls; Pat. No. 3,757,571, issued on Sept. 11, 1973, to Chamberas; and Pat. No. 3,839,907, issued on Oct. 8, 1974, to Hanson and Fineman.
Another economical and convenient test of internal combustion engines under simulated full-load conditions is the acceleration burst test in which an engine initially operating at idle speed is suddenly given full throttle and caused to accelerate to a maximum governed speed. The inertia of the engine is the load on the engine, and the time taken to accelerate through a low speed to a high speed is a measure of the full-power, full-load condition of the engine. This test is particularly useful for testing diesel engines, and provides a somewhat less accurate indication of the condition of a spark ignition engine equipped with a carburetor instead of fuel injectors.
The accuracy with which the full power condition of the engine is given by the time taken to accelerate from a low speed to a high speed depends on the accuracy of the speed measurements, which are in units of angular displacement (such as revolutions) divided by units of time (such as minutes or seconds). An accurate measurement of speed is complicated by the fact that the burst acceleration from a low speed to a high speed takes only about one second or less. Another complication has been found to be due to pulsations in instantaneous speed which are due to explosions and compressions in individual cylinders of the engine. The pulsations in instantaneous speed are particularly disturbing if they are non-uniform due to malfunctioning of one or more individual cylinders of the engine.